Such an arrangement is for example disclosed in U.S. Pat. No. 4,750,596, in which the retarding means that is used is arranged in a housing, having an opening through which the motor output shaft extends. The housing is mounted so as to float radially in a mounting which is provided for it in a casing. The housing has an annular rib for transverse engagement on the internal surface of the mounting. This rib, being formed by local thickening of the housing wall, is rigid.
However, because of the manufacturing tolerances that are unavoidable, a certain amount of clearance inevitably exists between the housing and its mounting, which results in some scope for transverse displacement of the housing to take place within the mounting.
The motor that is used in such an arrangement in practice is a stepping motor, which accordingly operates by pulsing action. On each pulse, and due to entrainment by friction effects, the housing of the retarding means is subjected to forces tending to displace it and therefore, once the clearance has been taken up, to bring it into contact with the internal surface of its mounting. This inevitably produces undesirable noise.